Self-test GFCI device with dual solenoid coil electronic control

ABSTRACT

A wiring device including a fault detection circuit, an actuating device, a first switching device, a second switching device, and a third switching device. The fault detection circuit is configured to detect one or more fault conditions and generate a trigger signal. The first switching device is activated to turn on when said trigger signal is received from said fault detection circuit. The second switching device includes a first pin, a second pin, and a third pin, said second switching device is electrically connected to a first conductive winding of the actuating device and said first switching device. The third switching device includes a first pin, a second pin, and a third pin, said third switching device is electrically connected to a second conductive winding of the actuating device and said first switching device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit to U.S. patent application Ser. No.14/156,036, filed on Jan. 15, 2014, the entire contents of which areincorporated herein by reference.

This application contains subject matter related to subject mattercontained in co-pending U.S. patent application Ser. No. 13/827,785,titled, “GFCI TEST MONITOR CIRCUIT,” by Stephen P. Simonin, U.S. patentapplication Ser. No. 13/422,797, titled, “SOLENOID COIL HAVING ANENHANCED MAGNETIC FIELD,” by Stephen P. Simonin, U.S. patent applicationSer. No. 13/422,790, titled, “ENHANCED AUTO-MONITORING CIRCUIT ANDMETHOD FOR AN ELECTRICAL DEVICE,” by Gaetano Bonasia and Kenny Padro andU.S. patent application Ser. No. 13/422,793, titled, “REINSTALLABLECIRCUIT INTERRUPTING DEVICE WITH VIBRATION RESISTANT MISWIREPROTECTION,” by Gaetano Bonasia et al., the entire contents of each ofwhich are expressly incorporated herein by reference, and each of whichis assigned to the same assignee as the instant application.

BACKGROUND Field

The present disclosure relates generally to switched electrical devices.More particularly, the disclosure is directed to control circuits forcircuit interrupting devices, such as self-testing ground fault circuitinterrupter (GFCI) devices, that switch to a “tripped” or unlatchedstate from a “reset” or latched state when one or more fault conditionsis detected. Control circuits consistent with the devices disclosedherein have self-testing capabilities that provide more robustend-of-life detection capabilities than are offered in current GFCIdevices.

Description of Related Art

GFCI devices having contacts that are biased toward the open positionrequire a latching mechanism for setting and holding the contacts in aclosed position. Likewise, switched electrical devices having contactsthat are biased toward the closed position require a latching mechanismfor setting and holding the contacts in an open position. Examples ofconventional types of devices include devices of the circuitinterrupting type, such as circuit breakers, arc fault interrupters andGFCIs, to name a few.

To be commercially sold in the United States a GFCI device must conformto standards established by the Underwriter's Laboratory (UL) inconjunction with industry-leading manufacturers as well as otherindustry members, such as various safety groups. One UL standardcovering GFCI devices is UL-943, titled “Standard for Safety-GroundFault Circuit Interrupters.” UL-943 applies to Class A, single- andthree-phase, GFCIs intended for protection of personnel and includesminimum requirements for the function, construction, performance, andmarkings of such GFCI devices. UL-943 requires, among other things,specific fault current levels and response timing requirements at whichthe GFCI device should trip. Typically, GFCIs are required to trip whena ground fault having a level higher than 5 milliamps (mA) is detected.Further, when a high resistance ground fault is applied to the device,the current version of UL-943 specifies that the device should trip andprevent electrical current from being delivered to the load inaccordance with the equation, T=(20/I)^(1.43), where “T” refers to themaximum amount of time it can take for the device to trip and isexpressed in seconds, and “I” refers to the minimum value of electricalcurrent causing the fault, and is expressed in milliamps (mA). Thus, inthe case of a 5 mA fault, the device must detect the fault and trip,i.e., prevent electrical current from flowing to the load, in 7.26seconds, or less.

With such safety-related standards in place, and because GFCI devicesare directly credited with saving many lives since their introduction inthe early 1970s, they have become ubiquitous throughout the residentialand commercial electrical power grid, not just in the United States, butworldwide. Like most electro-mechanical devices, however, GFCI devicesare susceptible to failure. For example, one or more of the electroniccomponents that drive the mechanical current interrupting device in aGFCI can short-out or otherwise become defective, as can components inthe fault detector circuit or elsewhere within the device. Suchcomponent failures can render the device unable to properly detect aground fault, and/or properly interrupt the flow of electrical currentwhen a fault is detected, thus, increasing the risk of potentiallylife-threatening injury.

Because of the susceptibility for component failure, it has long beenrequired that GFCI devices have a supervisory circuit that enablesmanual testing of the ability of the device to trip when a fault isencountered. Such supervisory circuits typically include a TEST buttonthat, when pressed, actuates a circuit that simulates a ground fault onthe hot and neutral conductors of the device. If the device isfunctioning properly, the simulated ground fault is detected and thedevice will trip, i.e., the mechanical interrupter is actuated. Thisopens the current path that connects the line side of the device, wherethe in AC power is supplied, and load side, where the user connects hisor her electrical appliance, etc., and also where downstream receptaclesor additional GFCI devices are connected.

A study performed several years ago by industry safety groups indicatedthat most often the public does not regularly test their GFCI devicesfor proper operation, i.e., by pressing the TEST button. This studyfurther revealed that some GFCI devices that had been in service for anextended period of time became non-functional and were unable toproperly detect a fault condition, thus, rendering the device unsafe.Specifically, it was discovered that after extended use GFCI devicesfail to trip when a fault occurs, thus rendering the device operable asan electrical receptacle only. That is, the device would provideelectrical power to the load contacts at all times and not be able totrip when a fault condition was present. Because GFCI devices were notbeing regularly tested, this unsafe condition became exacerbated. Moreparticularly, people falsely believed the device was operational, inview of the fact that it was adequately delivering power, when in factthe device was a potentially life-threatening hazard.

The discovery that GFCI devices deployed in the field are becomingincreasingly non-operational and unsafe in combination with therealization that people do not regularly test their GFCI devices,regardless of manufacturer's explicit instructions to do so, initiatedinvestigations into possible changes to the UL-943 standard, includingchanges that would require the GFCI devices to self-test (e.g.,auto-monitor) themselves without the need for human intervention. Thecontemplated changes to UL-943 further included a requirement for eithera warning to the consumer that the device could no longer provideprotection against a fault and/or a requirement that the deviceautomatically remove itself from service, e.g., permanently trip, whenthe self-test failed. Moreover, these additional self-testing operationswould have to be performed without interfering with the primary functionof the device, i.e., tripping when an actual fault was encountered.

The revised self-test functionality mentioned above is not yet arequirement for UL-943 certification, but it is expected that it will besoon. In preparation for this significant UL change, and in view of theseemingly endless reduction in the cost of integrated circuits, manyGFCI manufacturers have migrated to digital techniques (e.g.,microprocessors and microcontrollers) in favor of previous analogdesigns to provide both ground fault protection and self-monitoringfunctionality. The digital solutions offered thus far, however, are notideal. For example, several related art GFCI designs, including thosedirected at providing self-test functionality, suffer from nuisancetripping, a situation where the interrupter is actuated when neither areal ground fault, a manually generated simulated ground fault, nor anautomatic self-test fault are present. This unfavorable condition isbelieved by many to be worsened by the additional requirement ofautomatic self-testing, which often results in additional inductivecurrents being generated within the device.

It is therefore desired to provide a GFCI device that provides certainself-testing capabilities, including those proposed in the next revisionof UL-943, but minimizes the risks associated with nuisance tripping.

SUMMARY OF EXEMPLARY EMBODIMENTS

In consideration of problematic issues associated with related art GFCIdevices, including but not limited to the problematic issues discussedabove, a circuit in accordance with one or more exemplary embodimentsgenerally relates to an auto-monitoring circuit that continuouslymonitors the performance of a GFCI device. More specifically, aprocessing device, such as a microcontroller or microprocessor, isconfigured to periodically perform an auto-monitoring routine based on astored software program for testing and verifying the viability andfunctionality of various sub-circuits within the GFCI device. To testproper current isolation of the GFCI device, a driver coupled to themicrocontroller is operated to initiate a test signal representative ofa ground fault each time the auto-monitoring routine is performed, orrun, and different circuit nodes are monitored to confirm properoperation of the device.

A GFCI device in accordance with at least one embodiment uses aconventional 4141 GFCI chip, or some other appropriate integrateddevice, to activate a solenoid in the presence of a trip condition, asdetected by the sense and grounded neutral transformer coils. Similar tomost conventional GFCI devices, when a trip threshold is detected byeither of the transformer coils, a trigger signal is generated by the4141 chip to activate an SCR, i.e., the trigger signal turns the SCR ONsuch that current is conducted through a solenoid coil. An aspect of adevice in accordance with this and other embodiments utilizes dual-coilsin parallel that activate the solenoid plunger armature, also referredto herein as merely plunger or armature, with an enhanced magnetic fieldand, as a result, greater force is delivered to the plunger armaturethan would be delivered by a standard solenoid having a single coil.

Using two solenoid coils, however, requires additional designconsiderations. For example, it is not ideal to drive two independentSCRs with a single trigger signal generated by the 4141 chip becauseeach SCR causes inherent feedback during the time when the 4141 chip isfiring the trigger signal and driving two SCRs simultaneously causes acombined feedback that can damage the 4141 chip. To avoid thispotentially damaging feedback problem a device in accordance with one ormore embodiments includes a third SCR that blocks the feedback from thetwo coil-driving SCRs from reaching the 4141 chip trigger signal outputport. Thus, the design requirements for the 4141 chip are satisfied andboth coils can still be driven simultaneously. Another advantage of adevice consistent with one or more exemplary embodiments, as compared toconventional GFCI devices, is that separate independent firing of thecoil-driving SCRs can be performed. That is, according to another aspectof these embodiments, a gate signal from a microcontroller drives thetwo coil-driving SCRs under certain predetermined conditions whileblocking the trigger signal generated by the 4141 chip from interferingwith the gate signal.

An end-of-life indicator is also coupled to the microcontroller toindicate whether the GFCI device has failed to properly detect the testsignal or whether some other malfunction within the device has occurred.To avoid tripping the mechanical current-interrupting device when thetest signal is generated, but also allow as much of the GFCI devicecircuitry to perform its intended function, a unique monitor circuit isprovided that takes advantage of various functionality of the digitalcomponents, such as the GFCI integrated circuit device and themicrocontroller. Specifically, to provide an automatic test functionthat monitors the fault detection capability of the GFCI device withoutinterfering and causing a false trip under normal conditions,embodiments consistent with the invention include a specificallyselected filter capacitor associated with the interrupter drive outputof the GFCI integrated circuit (IC) device. Proper selection of thecapacitor and other related circuit components prevents the interrupterdrive circuit, e.g., silicon controlled rectifier (SCR), from firing, orturning ON, until a real fault condition is encountered.

In accordance with one aspect of exemplary embodiments a circuitinterrupting device is provided that includes one or more lineconductors for electrically connecting to an external power supply, oneor more load conductors for electrically connecting to an external load,an interrupting device connected to the line conductors and the loadconductors and electrically connecting the line conductors to the loadconductors when the circuit interrupting device is in a reset conditionand disconnecting the line conductors from the load conductors when thecircuit interrupting device is in a tripped condition.

A fault detection circuit is also provided that detects a faultcondition in the circuit interrupting device and generates a faultdetection signal when the fault condition is detected, wherein the faultdetection signal is provided to the interrupting device to place thecircuit interrupting device in the tripped condition. An auto-monitoringcircuit is electrically coupled to the fault detection circuit and theinterrupting device and continuously monitors one or more signals todetermine an operating state of the circuit interrupting device, whereinat least one of the monitored signals includes a first auto-monitoringinput signal the value of which is at least partially determined by avalue of a pre-trigger signal generated by the fault detection circuit,wherein the pre-trigger signal does not activate the interrupting deviceto place the circuit interrupting device in the tripped condition.

According to another aspect one or more exemplary embodiment, a circuitinterrupting device is provided that includes a wiring device having afault detection circuit configured to detect one or more faultconditions in the wiring device and generate a pre-trigger signal whenthe fault condition meets predetermined criteria, wherein the one ormore fault conditions includes a self-test fault condition. Aprogrammable circuit device is also provided that is programmed toexecute an auto-monitoring routine that includes the steps of generatinga self-test fault signal at a first output port of the programmablecircuit device, wherein the self-test fault signal generates a self-testfault condition in the wiring device, input the pre-trigger signal tothe programmable circuit device at a first input port, determining thevalue of the pre-trigger signal, processing the value of the pre-triggersignal, determining whether the fault detection circuit successfullydetected the self-test fault based on the processed value of thepre-trigger signal, incrementing a failure count if it is determinedthat the fault detection circuit failed to successfully detect theself-test fault and resetting the failure count if it is determined thatthe fault detection circuit did successfully detect the self-test fault.

According to a further aspect of exemplary embodiments, a method ofmonitoring the operational state of an electrical wiring device isprovided where the method includes the steps of periodically generatinga self-test fault signal, detecting the self-test fault signal,generating a pre-trigger signal when the self-test fault signal isdetected, incrementing a counter if the value of the pre-trigger signalis greater than or equal to a first threshold, resetting the counter ifthe value of the pre-trigger signal is less than the first threshold,determining that either a real fault condition or a simulated faultcondition has occurred if the value of the pre-trigger signal is greaterthan a second threshold less than the first threshold, ceasinggeneration of the self-test fault signal if it is determined that eithera real fault condition or a simulated fault condition has occurred, andcontinuing generation of the self-test fault signal if it is determinedthat either a real fault condition or a simulated fault condition hasnot occurred.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the disclosed method and device are describedin detail below by way of example, with reference to the accompanyingdrawings, in which:

FIG. 1 is a side elevation view of a self-testing GFCI receptacle devicein accordance with an exemplary embodiment;

FIG. 2 is a side elevation view of the self-testing GFCI receptacleshown in FIG. 1 with the front cover of the housing removed;

FIG. 3 is a side elevation view of a core assembly of the self-testingGFCI receptacle device shown in FIG. 1;

FIGS. 4A-4D is a schematic of an exemplary circuit consistent with anexemplary embodiment;

FIG. 5 is an elevation view of a dual-coil solenoid used in connectionwith a GFCI receptacle in accordance with an exemplary embodiment;

FIG. 6 is sectional (cutaway) view of the dual-coil solenoid of FIG. 5with bobbin and plunger shown.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments include one or more of the novel mechanical and/orelectrical features described in detail below. For example, one or moreof the exemplary embodiments disclosed include auto-monitoring or,self-test, features. Some self-test features and capabilities withrespect to GFCI devices have been disclosed previously, for example, inU.S. Pat. Nos. 6,807,035, 6,807,036, 7,315,437, 7,443,309 and 7,791,848,and U.S. patent application Ser. No. 13/422,790, filed on Mar. 16, 2012,all which are commonly assigned to the same assignee as this applicationand the entire respective contents of which are incorporated herein byreference for all that is taught. An auto-monitoring feature consistentwith the method and devices disclosed herein is more robust than thatwhich has been previously disclosed and reduces the probability of falseor nuisance tripping by the device. For example, additional features areprovided that relate to the determination of an end-of-life (EOL)condition and actions taken subsequent to such determination. Furtherexemplary novel electrical and mechanical features are described hereinbelow with reference to the figures.

Referring to FIG. 1, a GFCI receptacle 10 according to an exemplaryembodiment includes a front cover 12 having a duplex outlet face 14 withphase 16, neutral 18 and ground 20 openings. Face 14 also has opening 22accommodating RESET button 24 adjacent to opening 26 accommodating TESTbutton 28, and six respective circular openings, 30-35. In accordancewith this exemplary embodiment openings 30, 33 accommodate tworespective indicators, such as different colored LEDs, openings 32, 34accommodate respective bright LEDs used, for example, as a nightlight,opening 31 accommodates a photoconductive photocell used, for example,to control the nightlight LEDs, and opening 35 provides access to a setscrew for adjusting a photocell device in accordance with this and otherexemplary embodiments. Rear cover 36 is secured to front cover 12 byeight fasteners 38—four of the eight fasteners 38 are shown in FIG. 1and the four additional fasteners 38 are provided on the side ofreceptacle 10 obscured from view in FIG. 1. For example, each fastener38 may include a barbed post 50 on front cover 12 and correspondingresilient hoop 52 on rear cover 36, similar to that which is describedin detail in U.S. Pat. No. 6,398,594, the entire contents of which areincorporated herein by reference for all that is taught. Groundyoke/bridge assembly 40 having standard mounting ears 42 protrudes fromthe ends of receptacle 10.

Referring to FIG. 2, front cover 12 of GFCI receptacle 10 has beenremoved to expose manifold 126, which provides support for printedcircuit board 390 and yoke/bridge assembly 40. According to theembodiment shown, manifold 126 includes four dovetail interconnects 130that mate with corresponding cavities 132 along the upper edge of rearcover 36. One dovetail-cavity pair is provided on each of the four sidesof manifold 126 and rear cover 36, respectively.

FIG. 3 is a side elevation view of core assembly 80. Core assembly 80includes circuit board 82 that supports most of the working componentsof the receptacle device, including the circuit shown in FIGS. 4A-4D,sense transformer 84 and grounded neutral transformer 85 (not shown).Line contact arms 94, 96 pass through transformers 84, 85 with aninsulating separator 98 therebetween. Line contact arms 94, 96 arecantilevered, their respective distal ends carrying phase and neutralline contacts 102, 104. Load contact arms 98, 100 are also cantileveredwith their respective distal ends carrying phase and neutral loadcontacts 101, 103. The resiliency of the cantilevered contact armsbiases the line contacts 102, 104 and load contacts 101, 103 away fromeach other, thus keeping the contacts electrically isolated from eachother under normal conditions. At or near their respective distal ends,load contact arms 98, 100 rest on a movable contact carriage 106, madeof insulating (preferably thermoplastic) material.

FIGS. 4A-4D, hereafter collectively referred to as FIG. 4, is aschematic drawing of the electro-mechanical components of a GFCIreceptacle device consistent with one or more of the exemplaryembodiments. According to these embodiments, the circuit shown in FIG. 4is employed in a GFCI device as described above. The circuit of FIG. 4is consistent with the mechanical operation of the exemplary embodimentsdescribed above; however, a GFCI device consistent with theseembodiments need not employ the precise electrical circuit depicted inFIG. 4 and those of ordinary skill in the art, after viewing FIG. 4and/or reviewing the description set forth below, would be able tomodify certain aspects of the circuit to achieve similar overallresults. Such modifications are contemplated and believed to be withinthe scope of the invention set forth herein.

The circuit shown in FIG. 4, or various sub-circuits thereof, can beimplemented in a variety of electrical wiring devices. For purposes ofdescription here, however, the circuit of FIG. 4 is discussed inconjunction with its use in the GFCI receptacle device shown in FIGS.1-3.

The circuit shown in FIG. 4 includes phase line terminal 326 and neutralline terminal 328 for electrical connection to an AC power source (notshown), such as a 60-hertz, 120 Volt RMS power source used in the UnitedStates for mains power in connection with both residential andcommercial applications. The circuit of FIG. 4 and software residentwithin one or more components of the circuit can be modified toaccommodate other power delivery systems as well. Such modifications andthe resultant circuit and wiring devices in which the circuit andsoftware would be implemented are contemplated by the inventor andconsidered to be within the spirit and scope of the invention describedherein. For example, power delivery systems that use different voltagesand frequencies are within the scope of the invention.

Referring to FIG. 4, phase conductor 330 and neutral conductor 332 arerespectively connected to the phase and neutral line terminals and eachpasses through sense transformer 334 and grounded neutral transformer336, both of which are part of a detection circuit described below. Byway of example, phase and neutral line terminals correspond to inputterminal screws 326, 328 in FIG. 1 and phase and neutral line conductors330, 332 represent line contact arms 94, 96, respectively, as describedabove with respect to FIG. 3. Each of line conductors 330, 332 has arespective fixed end connected to the phase and neutral line terminalsand each includes a respective movable contact, e.g., contacts 102, 104from the embodiment described above. Face phase and face neutralconductors 338, 340, respectively, include electrical contacts (notshown) fixed thereto. The face conductors are electrically connected toand, in the embodiment shown, are integral with, respective faceterminals 342, 344, to which plug blades from a load device (not shown),such as an electrical appliance, would be electrically connected whenthe electrical receptacle device is in use.

The circuit shown in FIG. 4 according to this embodiment also includesoptional load phase and load neutral terminals 346, 348, respectively,which electrically connect to a downstream load (not shown), such as oneor more additional receptacle devices. Load terminals 346, 348 arerespectively connected to cantilevered load conductors 227, 228, each ofwhich includes a movable contact (not shown in FIG. 4) at its distalend. The load contacts are disposed below respective phase and neutralline contacts and phase and neutral face contacts and are coaxial withthem such that when the line conductors are moved toward the load andface conductors, the three sets of contacts mate and are electricallyconnected together. When the device is in this condition it is said tobe “reset” or in the reset state.

The Detector Circuit

With continued reference to FIG. 4, detector circuit 352 includestransformers 334, 336 as well as a GFCI integrated circuit device (GFCIIC), 350. In accordance with the present embodiment GFCI IC 350 is thewell-known 4141 device, such as an RV4141 device made by FairchildSemiconductor Corporation. Other GFCI IC devices could potentially beused in the circuit of FIG. 4 instead of the 4141 device and such amodification is within the spirit and scope of the method and devicesdisclosed herein.

GFCI IC device 350 receives electrical signals from various othercircuit components, including transformers 334, 336, and detects one ormore types of faults, such as a real ground fault, a simulated groundfault or a self-test ground fault, as well as a real or simulatedgrounded neutral fault. For example, when a sufficient current imbalancebetween line conductors 330, 332 occurs, a net current flows through thetransformers 334, 336, causing a magnetic flux to be created about atleast transformer 334. This magnetic flux results in electrical currentbeing induced on conductor 333, which is wound around sense transformer334. Respective ends of conductor 333 are connected to the positive andnegative inputs to the sense amplifier of GFCI IC device 350 at inputports V-REF and VFB, respectively. The induced current on conductor 333causes a voltage difference at the inputs to the sense amplifier of GFCIIC 350. When the voltage difference at the inputs to the sense amplifierof GFCI IC 350 exceeds a predetermined threshold value, a detectionsignal is generated at one or more output ports of GFCI IC 350, such asthe SCR trigger signal output port (SCR_OUT). The threshold value usedby GFCI IC 350 is determined by the effective resistance connectedbetween the op-amp output (OP_OUT) and the positive input to the senseamplifier (VFB).

The current imbalance on line conductors 330, 332 typically results fromeither a real ground fault, a simulated ground fault or a self-testground fault. A simulated ground fault is generated when test switch 354(FIG. 4B) closes, which occurs when TEST button 28 (FIG. 1) is pressedby the user. As described in further detail below, a self-test faultoccurs when auto-monitoring circuit 370 (FIG. 4D) initiates anauto-monitoring test sequence that includes an electrical current beinggenerated on independent conductor 356 (FIG. 4A).

According to the present embodiment, when test switch 354 closes, someof the current flowing in line conductors 330, 332 and load conductors338, 340 is diverted from the phase face conductor 338 (and phase loadconductor 277 when the device is in the reset state) around sensetransformer 334 and through resistor 358 to neutral line conductor 332.By diverting some of the current through resistor 358 in this manner, animbalance is created in the current flowing through conductor 330 andthe current flowing in the opposite direction through conductor 332.When the current imbalance, i.e., the net current flowing through theconductors passing through the sense transformer, exceeds a thresholdvalue, for instance 4-5 milliamps, this simulated ground fault isdetected by detector circuit 352 and the SCR drive output of GFCI IC 350(SCR_OUT) is activated.

When the SCR drive output of GFCI IC 350 is activated, the gate of SCR3360 is turned ON allowing current to flow from the phase line conductor330 through diode 359, a resistor network R15, R3, R19, and SCR3 360.The current flowing through SCR3 360 generates a voltage at, and turnsON, the gates of SCR1 361 and SCR2 369. When SCR1 361 is turned ON,current flows from phase line conductor 330 through secondary coil 363of dual-coil solenoid 362, fuse 365, diode 367 and SCR1 361. Further,when SCR2 369 is turned ON, current flows from phase line conductor 330through primary coil 364 of dual-coil solenoid 362, fuse 372, diode 374and SCR2 369. The current flowing through each of coils 363, 364generates a magnetic field that moves an armature within solenoid 362.

When the solenoid armature moves, it unlatches a contact carriage,(e.g., 106 in FIG. 3) which is part of interrupting device 315, and thecarriage drops under the natural bias of line conductors 330, 332, thatis, away from the face conductors 338, 340 and load conductors 277, 278.The device is now said to be “tripped,” as a result of the successfulmanually generated simulated fault test sequence, and the device willnot deliver power to a load until it is reset, i.e., by pressing theRESET button. The time it takes from the instant switch 354 closes untilthe device is tripped and current no longer flows from phase lineconductor 330 to either the face and load conductors and throughsolenoid coils 363, 364, is so short that fuses 365, 372 remain intact.

According to the present embodiment, GFCI IC 350 is a conventional 4141chip. Similar to most conventional GFCI devices, when a trip thresholdis detected by either of the transformer coils, 334, 336, a triggersignal is generated by the 4141 chip to activate an SCR, i.e., thetrigger signal turns the SCR ON such that it conducts current through asolenoid coil. An aspect of a device in accordance with this and otherembodiments utilizes dual coils in parallel that activate the solenoidplunger with an enhanced magnetic field and, as a result, greater forceis delivered to the plunger than would be delivered by a standardsolenoid having a single coil.

Referring to FIGS. 5 and 6, a dual-coil solenoid according to at leastone exemplary embodiment includes a bobbin 1100 with a hollow center anda metal armature, or plunger 1105, therein. The solenoid 600, shown inFIG. 5 without a bobbin, illustrates the beginning and ending of therespective coils or windings. As shown, solenoid 600 includes a primarywinding 602 that has a starting end and a terminating end distal fromthe starting end. Primary winding 602 imparts a first magnetic forcewhen the primary winding is electrically energized. Solenoid 600 alsoincludes a secondary winding 604 with a starting end and a terminatingend distal from the starting end that is wound on top of the primarywinding 602. Secondary winding 604 imparts a second magnetic force whenthe secondary winding is electrically energized. When the primary andsecondary windings are energized simultaneously, a third magnetic forceis imparted on the plunger.

The third magnetic force which is generated when both the first andsecond coils are energized simultaneously is significantly greater thanthe combination of the first and second magnetic forces. For example,referring to FIG. 6, a dual-coil solenoid is wound on bobbin 1100 inaccordance with at least one embodiment. Secondary winding 1104comprising 950 turns of 33 AWG wire is wound directly on top of primarywinding 1102 which comprises 800 turns of 35 AWG wire. As shown, bothwindings are wound on bobbin 1100 which includes cylindrical plunger1105 disposed within a hollow cavity of the bobbin.

When a solenoid consistent with the one described above was tested, acombined magnetic force of 5.5 lbs. was generated. Specifically, whenonly the primary winding 1102 was energized it produced 2.5 lbs. offorce on plunger 1105 and when only the secondary winding 1104 wasenergized; it produced 1.4 lbs. of force on the plunger 1105. However,when both the primary and the secondary windings were energizedtogether, i.e., at the same time, a total of 5.5 lbs. of force wasimparted on plunger 1105, which is an approximate 42% improvement indelivered force over the mere combination, i.e., sum, of the twoindependent forces. As a result, it is possible to drive theplunger/armature with greater force than is otherwise available when asingle winding solenoid is employed or when a redundant coil design isemployed and only one or the other winding is energized at any giventime. Increasing the delivered magnetic force on the plunger providesadvantages such as a higher probability of opening the contacts when,for example, the contacts have welded together. Further details ofsolenoid 600 and other various configurations thereof, consistent withthe present invention, can be found in co-pending U.S. patentapplication Ser. No. 13/422,797, the entire contents of which areincorporated herein by reference.

In regard to the above embodiment, it has further been observed that aneven stronger combined magnetic force can be achieved on plunger 1105under certain operating conditions; for example, magnetic forces of upto 12 lbs. have been observed. For example, as discussed in severalother places within this disclosure, during normal operation of a GFCIdevice the solenoid is activated by the GFCI IC device 350 (FIG. 4) todrive the plunger such that the interrupter mechanically trips, thusseparating the electrical contacts of the device. If a failure occurswithin the device, however, such as SCR3 creating an open-circuit, theGFCI IC device 350 will be unable to activate the solenoid, for example,by driving the gate of SCR3.

According to the present embodiment, as well as others, programmabledevice 301 detects this condition and independently drives therespective SCRs, e.g., SCR1 and SCR2 in FIG. 4. If the device does nottrip the first time programmable device 301 drives the SCRs, the plungerin the solenoid is biased, e.g., by a spring or some other force, backto its original, static, position within the solenoid. Due to the timingof the drive signal provided by programmable device 301, as controlledby its resident software, a subsequent drive signal is provided at theprecise time the plunger is being biased in this reverse direction, andis in motion in a direction opposite the magnetic force of the solenoid.As a result, a magnetic force much greater than when the plunger isactuated from its static position is imparted on the plunger. Forexample, as mentioned, a magnetic force of approximately 12 lbs. hasbeen measured under these conditions. Although this condition is afailure condition and would not occur when the device is operatingnormally, it provides a situation where the contacts are driven with aneven stronger force to open, e.g., in the event the contacts are weldedor otherwise unable to separate. According to this embodiment, theprogrammable device 350 detects this situation as an end-of-life (EOL)condition and activates one or more of an audio and visual indication,for example, by activating PCB 390 in FIG. 4.

Using two parallel solenoid coils in the GFCI detection circuit asdiscussed above, however, requires additional design considerations. Forexample, it is not ideal to drive two independent SCRs with a singletrigger signal generated by the 4141 chip. Specifically, each SCR causesinherent feedback during the time when the 4141 chip is firing thetrigger signal. Thus, driving two SCR devices simultaneously causes acombined feedback that can possibly damage the 4141 chip. Referringagain to FIG. 4, to avoid this potentially damaging feedback problem aGFCI device in accordance with embodiments of the present inventionincludes a third SCR, e.g., SCR3 360 in the embodiment described above.The third SCR blocks the feedback from the two coil-driving SCRs, e.g.,SCR1 361 and SCR2 369 in the above embodiment, from reaching the 4141chip trigger signal output port, e.g., SCR_OUT.

Thus, by including the third SCR between the GFCI IC device and thecoil-driving SCRs, the design requirements for the GFCI IC device aresatisfied and both coils can be driven simultaneously. Another advantageof a device consistent with exemplary embodiments, as compared toconventional GFCI devices, is that separate independent firing of thecoil-driving SCRs can be performed. In particular, a gate signal from amicrocontroller drives the two coil-driving SCRs under certainpredetermined conditions while blocking the trigger signal generated bythe 4141 chip from interfering with the gate signal. I/O port GP2 ofprogrammable device 301 can be programmed to activate the respectivegates of SCR1 361 and SCR2 369. When these two SCRs fire and conductelectrical current, the third SCR, i.e., SCR3 360 blocks any feedbackfrom SCR1 361 and SCR2 369 from damaging the SCR drive port (SCR_OUT) ofGFCI IC device 350.

Manual Testing Via the Reset Operation

Referring to FIG. 4, closing reset switch 300, e.g., by pressing RESETbutton 24 (FIG. 1), also initiates a test operation. Specifically, whenreset switch 300 closes, a voltage supply output, VS, of GFCI IC 350 iselectrically connected to the gate of SCR 360 through conductor 308,thus, turning ON SCR 360. When SCR 360 is turned ON, current is drawnfrom line conductor 330 through diode 359 and SCR 360 and ultimately toground. Similar to when SCR 360 is turned ON by pressing the TESTbutton, as discussed previously, turning ON SCR 360 by pressing theRESET button results in SCR 361 and SCR 369 also being turned ON andcurrent flowing through solenoid coils 363, 364. The current flowingthrough coils 363, 364 of solenoid 362 generates a magnetic field at thesolenoid and the armature within the solenoid is actuated and moves.Under typical, e.g., non-test, conditions, the armature is actuated inthis manner to trip the device, such as when an actual fault occurs.

When reset switch 300 closes, however, the device is likely already inthe tripped condition, i.e., the contacts of the line, face and loadconductors are electrically isolated. That is, the RESET button isusually pressed to re-latch the contact carriage and bring the line,face and load contacts back into electrical contact after the device hastripped. If the armature of solenoid 362 fails to fire, i.e., move, whenthe RESET button is pressed, and the reset mechanism, including thecontact carriage, fails to engage the reset plunger on its return afterthe RESET button is released, the device will not reset. Accordingly,if, for example, the device has not been wired to the AC power lines, orit has been mis-wired, that is, the device has been wired with the ACpower not connected to the line terminals, 326, 328, no power is appliedto the GFCI IC 350. If no power is applied to GFCI IC 350, the gate ofSCR 360 cannot be driven, either by the SCR output of GFCI IC 350 orwhen the RESET button is pressed. Under this condition the device willnot be able to be reset. The mis-wire condition is prevented inaccordance with a wiring device consistent with the present embodimentby ensuring the device is shipped to the user in the tripped condition.Because the device cannot be reset until AC power is properly applied tothe line terminals, the mis-wire condition is prevented.

The Auto-Monitoring Circuit

With continued reference to the exemplary circuit schematic shown inFIG. 4, auto-monitoring circuit 370 includes a programmable device 301.Programmable device 301 can be any suitable programmable device, such asa microprocessor or a microcontroller, which can be programmed toimplement the auto-monitoring routine as explained in detail below. Forexample, according to the embodiment shown in FIG. 4, programmabledevice 301 is implemented by an ATMEL™ microcontroller from the ATtiny10 family. It could also be implemented by a Microchip microcontrollersuch as a PIC10F204/206.

According to one exemplary auto-monitoring, or automatic self-testing,routine in accordance with the embodiment shown in FIG. 4,microcontroller 301 initiates the auto-monitoring routine approximatelyevery three (3) seconds by setting a software auto-monitoring test flag.The auto-monitoring test flag initiates the auto-monitoring routinewithin the circuit interrupting device and confirms that the device isoperating properly or, under certain circumstances, determines that thecircuit interrupting device has reached its end-of-life (EOL). When theauto-monitoring routine runs with a positive, i.e., successful, result,the auto-monitoring circuit enters a hibernation state untilmicrocontroller 301 sets the test flag again and initiates anotherauto-monitoring routine.

If the auto-monitoring routine runs with a negative result, e.g., itcannot be determined that the circuit interrupting device is functioningproperly or it determines that it is, in fact, not operating properly, afailure counter is incremented and microcontroller 301 initiates anotherauto-monitoring routine when instructed by the software program storedin memory within the device. In addition to the failure count beingincremented, a temporary indication of the failure is also provided. Forexample, according to the present embodiment, when such a failureoccurs, I/O port GP0 of microcontroller 301 is controlled to be anoutput and light emitting diode (LED) 376 is controlled to flash, e.g.,one or more times, to indicate the failure to a user. If the failurecounter reaches a predetermined value, i.e., the auto-monitoring routineruns with a negative result a certain number of times, the number beingstored and implemented in software, the auto-monitoring routine invokesan end-of-life (EOL) sequence. The EOL sequence includes one or more ofthe following functions; (a) indicate that EOL has been reached, forexample, by continuously flashing or illuminating an indicator lightand/or generating an audible sound, (b) attempt to trip the device, (c)prevent an attempt to reset the device, (d) store the EOL event onnon-volatile memory, e.g., in the event there is a power failure, and(e) clear the EOL condition when the device is powered down.

In accordance with this embodiment, when the auto-monitoring softwaredetermines it is time to run the auto-monitoring routine, i.e., based onthe auto-monitor timer, a stimulus signal 302 is turned ON at I/O portGP1 of microcontroller 301. When the stimulus signal is turned ON,electrical current flows through resistor 303 and a voltage isestablished at the base of transistor 304, turning the transistor ON.When transistor 304 is turned ON, current flows from dc voltage supply378 through resistor 305, which is, for example, a 3k-ohm resistor, andcontinues through electrical conductor 356 and transistor 304 to ground.Regarding dc voltage source 378, according to the present embodiment thevalue of this voltage source is designed to be between 4.1 and 4.5 voltsdc, but the value of this voltage supply can be any other suitable valueas long as the value used is adequately taken into account for othercircuit functionality described below.

According to this exemplary embodiment, electrical conductor 356 is awire, but it could also be a conductive trace on a printed circuitboard. Conductor 356 is connected at one end to resistor 305, traversesthrough sense transformer 334 and is looped approximately ten (10) timesaround the core of the transformer and connected at its other end to thecollector of transistor 304. Thus, when the software auto-monitoringtest flag is set in microcontroller 301 and transistor 304 is turned ON,current flows through conductor 356 which comprises an independentconductor separate from phase line conductor 330 and neutral lineconductor 332, which also traverse through the center of sensetransformer 334.

If the circuit interrupting device according to the present embodimentis functioning properly, as current flows through conductor 356 andthrough the sense transformer a magnetic flux is generated at sensetransformer 334. The flux generates a signal on conductor 333 which isdetected by detection circuit 352, including GFCI IC device 350. Inaccordance with this embodiment, when device 350 detects the fluxcreated at sense transformer 334, a voltage level is increased at one ofthe I/O ports of device 350, for example at the output port labeled CAPin FIG. 4, thus increasing the voltage on conductor 306.

According to this embodiment, capacitor 307 is connected between the CAPI/O port of microcontroller 301 and ground. As is known in the art,attaching a capacitor directly between the CAP output of a 4141 GFCI ICdevice and ground causes the SCR trigger signal (SCR_OUT) output fromGFCI IC device 350 to be delayed by a predetermined period of time. Theamount of time the trigger signal is delayed is typically determined bythe value of the capacitor. According to the present embodiment,however, capacitor 307 is not connected directly between the CAP outputand ground. Instead, capacitor 307 is also connected to the ADC I/O portGP0 of microcontroller 301 via a circuit path that includes diode 310 inseries with resistor 311, e.g., 3 M-Ohm, which completes a voltagedivider circuit with resistor 312, e.g., 1.5 M-Ohm. This additionalcircuitry connected to the capacitor at the CAP output of GFCI IC device350 drains current from the delay capacitor.

By measuring the value of the signal at ADC I/O port (GP0) andconfirming it is above a certain level, it can be determined whether ornot the self-test fault signal generated on conductor 356 was properlydetected by detection circuit 352 and it can further be confirmedwhether GFCI IC device 350 is capable of generating the appropriate SCRtrigger signal. Also, to avoid tripping the device during a self-testauto-monitoring fault, the voltage at capacitor 307 is measured andproper self-test fault detection is confirmed before a drive signal isoutput at SCR_OUT of GFCI IC device 350.

If the current drain on capacitor 307 is too high, GFCI IC device 350may not operate properly. For example, if as little as 3-4 microamps(μA) of current is drained from capacitor 307, grounded neutralconditions, which are also intended to be detected by GFCI IC device350, may not be accurately detected, e.g., pursuant to UL requirements,because the SCR trigger signal (SCR_OUT) will not fire within thenecessary amount of time. According to the present embodiment, less thanabout 1.3 microamps, or about 5% of the specified delay current for theGFCI IC device 350, is drained for the ADC I/O port GP0 ofmicrocontroller 301. This small current drain from capacitor 307 has noeffect on the ability of the device to properly detect real groundfaults and/or real grounded neutral faults.

According to this embodiment, approximately 50 nanoamps (nA) of currentis drawn off of capacitor 307. Parallel resistors 311 and 312 connectedto the ADC I/O port GP0 of microcontroller 301 create a 4.5 megaohm (MΩ)drain which limits the current pulled from capacitor 307 to a maximum of1.0 microamp. GFCI IC device 350 uses approximately 40 microamps ofcurrent to generate the SCR trigger but microcontroller 301 onlyrequires approximately 50 nanoamps to read the SCR trigger signal off ofcapacitor 307 before the SCR trigger signal is output from SCR_OUT.Accordingly, by selecting the proper value for capacitor 307, inconjunction with appropriate value selections for resistors 311 and 312,as well as diode 310, it is possible to maintain the correct delay forthe SCR trigger signal (SCR_OUT) from GFCI IC device 350 and use the ADCin microcontroller 301 to measure the signal at ADC input (GP0) todetermine whether the test signal on conductor 356 has been properlydetected by detection circuit 352.

It should also be noted that in the embodiment shown in FIG. 4, LED 376is also connected to ADC I/O port (GP0) of microcontroller 301.Accordingly, whether or not LED 376 is conducting or not will affect thedrain on capacitor 307, as well as the delay of the SCR trigger signaland the ability of microcontroller 301 to properly measure the signaloutput from the CAP I/O port of GFCI IC device 350. Thus, in regard tothe circuit shown in FIG. 4, LED 376 is selected such that it does notturn ON and begin conducting during the time microcontroller 301 ismeasuring the signal from the CAP output of GFCI IC device 350. Forexample, LED 376 is selected such that its turn-ON voltage is about 1.64volts, or higher which, according to the circuit shown in FIG. 4, can bemeasured at I/O port GP0. Additionally, to prevent any signal adding tocapacitor 307 when LED 376 is being driven, diode 310 is provided.

According to this embodiment, the circuit path that includes diode 310and the voltage divider, 311, 312, is connected to I/O port GP0 ofmicrocontroller 301, which serves as an input to an analog-to-digitalconverter (ADC) within microcontroller 301. The ADC of microcontroller301 measures the increasing voltage established by the charging actionof capacitor 307. When a predetermined voltage level is reached,microcontroller 301 turns OFF the auto-monitoring stimulus signal 302which, in turn, turns OFF transistor 304, stopping the current flow onconductor 356 and, thus, the flux created at sense transformer 334. Whenthis occurs, it is determined by microcontroller 301 that a qualifiedauto-monitoring event has successfully passed and the auto-monitoringfail counter is decremented if the present count is greater than zero.

In other words, according to this embodiment an auto-monitoring routineis repeated by microcontroller 301 on a predetermined schedule. Based onthe software program stored in memory within microcontroller 301, theauto-monitoring routine is run, as desired, anywhere from every fewseconds to every month, etc. When the routine is initiated, the fluxcreated at sense transformer 334 occurs in similar fashion to the mannerin which flux would be created if either an actual ground fault hadoccurred or if a simulated ground fault had been manually generated,e.g., by pressing the TEST button as described above.

There is a difference, however, between an auto-monitoring (self-test)fault generated by the auto-monitoring routine and either an actualground fault or a simulated fault generated by pressing the TEST button.When either an actual or simulated ground fault occurs, a difference inthe current flowing in the phase and neutral conductors, 330 and 332,respectively, should be generated. That is, the current on conductor 330should be different than the current on conductor 332. This differentialcurrent flowing through sense transformer 334 is detected by GFCI ICdevice 350, which drives a signal on its SCR_OUT I/O port to activatethe gate of SCR 360 and turn it ON. When SCR 360 turns ON, current isdrawn through coils 363, 364 which causes interrupting device 315 totrip, causing the contact carriage to drop which, in turn, causes theline, face and load contacts to separate from each other. Thus, currentis prevented from flowing through phase and neutral conductors 330, 332to the phase and neutral face terminals 342, 344, and the phase andneutral load terminals 346, 348, respectively.

In comparison, when the auto-monitoring routine is performed inaccordance with the present invention, no differential current iscreated on the phase and neutral conductors 330, 332 and theinterrupting device 315 is not tripped. Instead, during theauto-monitoring routine, the flux generated at sense transformer 334 isa result of current flowing through conductor 356, which is electricallyseparated from phase and neutral conductors 330, 332. The currentgenerated on conductor 356 is present for only a brief period of time,for example, less than the delay time established by capacitor 307,discussed previously.

If the voltage established at the input to the ADC input (GP0) ofmicrocontroller 301 reaches a programmed threshold value within thispredetermined period of time during an auto-monitoring routine, it isdetermined that the detection circuit 352 successfully detected thecurrent flowing through the core of sense transformer 334 and theauto-monitoring event is deemed to have passed. Microcontroller 301,thus, determines that detection circuit 352, including GFCI IC device350, is working properly. Because the current flowing through sensetransformer 334 during the auto-monitoring routine is designed to besubstantially similar in magnitude to the differential current flowingthrough the transformer during a simulated ground fault, e.g., 4-6milliamps, it is determined that detection circuit 352 would be able todetect an actual ground fault and provide the proper drive signal to SCR360 to trip interrupter 315.

Alternatively, auto-monitoring circuit 370 might determine that theauto-monitoring routine failed. For example, if it takes longer than thepredetermined period of time for the voltage at the ADC input at GP0 ofmicrocontroller 301 to reach the given voltage during theauto-monitoring routine, it is determined that the auto-monitoring eventfailed. If this occurs, an auto-monitoring fail tally is incremented andthe failure is indicated either visually or audibly. According to oneembodiment, the ADC port (GP0) of microcontroller 301 is converted to anoutput port when an auto-monitoring event failure occurs and a voltageis placed on conductor 309 via I/O port GP0, which is first converted toa output port by the microcontroller. This voltage at GP0 generates acurrent on conductor 309 that flows through indicator LED 376 andresistor 380 to ground. Subsequently, ADC I/O port (GP0) ofmicrocontroller 301 is converted back to an input port and remains readyfor the next scheduled auto-monitoring event to occur.

According to this embodiment, when an auto-monitoring event failureoccurs, indicator LED 376 illuminates only for the period of time whenthe I/O port is converted to an output and an output voltage isgenerated at that port; otherwise LED 376 remains dark, ornon-illuminated. Thus, if the auto-monitoring routine is run, forexample, every three (3) seconds, and an event failure occurs only asingle time or sporadically, the event is likely to go unnoticed by theuser. If, on the other hand, the failure occurs regularly, as would bethe case if one or more of the components used in the auto-monitoringroutine is permanently disabled, indicator LED 376 is repetitivelyturned ON for 10 msec and OFF for 100 msec by microcontroller 301, thusdrawing attention to the device and informing the user that criticalfunctionality of the device has been compromised. Conditions that causethe auto-monitoring routine to fail include one or more of thefollowing, open circuited differential transformer, closed circuiteddifferential transformer, no power to the GFCI IC, open circuitedsolenoid, SCR trigger output of the GFCI IC continuously high, and SCRoutput of the GFCI IC continuously low.

According to a further embodiment, if the auto-monitoring fail tallyreaches a predetermined limit, for example, seven (7) failures withinone (1) minute, microcontroller 301 determines that the device is nolonger safe and has reached its end-of-life (EOL). If this occurs, avisual indicator is activated to alert the user that the circuitinterrupting device has reached the end of its useful life. For example,when this EOL state is determined, the ADC I/O port (GP0) ofmicrocontroller 301 is converted to an output port, similar to when asingle failure is recorded as described above, and a signal is eitherperiodically placed on conductor 309 via GP0, i.e., to blink LED 376 ata rate of, for example, 10 msec ON and 100 msec OFF, or a signal iscontinuously placed on conductor 309 to permanently illuminate LED 376.The auto-monitoring routine is also halted at this time.

In addition to the blinking or continuously illuminated LED 376,according to a further embodiment when EOL is determined, an optionalaudible alarm circuit 382 on printed circuit board (PCB) 390 is alsoactivated. In this situation the current through LED 376 establishes avoltage on the gate of SCR 384 such that SCR 384 is turned ON, eithercontinuously or intermittently, in accordance with the output signalfrom GP0 of microcontroller 301. When SCR 384 is ON, current is drawnfrom phase line conductor 330 to activate audible alarm 386 (e.g., abuzzer) providing additional notice to a user of the device that thedevice has reached the end of its useful life, i.e., EOL. For example,with respect to the present embodiment, audible alarm circuit 382includes a parallel RC circuit including resistor 387 and capacitor 388.As current is drawn from phase line conductor 330, capacitor 388 chargesand discharges at a rate controlled by the value of resistor 387 suchthat buzzer 386 sounds a desired intermittent alarm.

A further aspect of this embodiment includes dimmable LED circuit 396.Circuit 396 includes transistor 398, LEDs, 400, 402, light sensor 404(e.g., a photocell) and resistors 406-408. When the ambient light, e.g.,the amount of light in the vicinity of the circuit interrupting deviceaccording to the present embodiment, is rising, light sensor 404 reactsto the ambient light level to apply increasing impedance to the base oftransistor 398 to dim the LEDs as the ambient light increases.Alternatively, when the ambient light decreases, e.g., as night beginsto fall, the current flowing through sensor 404 increases, accordingly.As the ambient light level decreases, LEDs 400 and 402 illuminatebrighter and brighter, thus providing a controlled light level in thevicinity of the device.

A further aspect of the embodiment shown in FIG. 4 includes a mechanismfor providing microcontroller 301 with data related to whether thedevice is tripped or in the reset condition. As shown in FIG. 4,opto-coupler 392 is connected between phase and neutral load conductors277, 278 and I/O port (GP3) of microcontroller 301. Microcontroller 301uses the value of the signal (voltage) at port GP3 to determine whetheror not GFCI IC device 350 is being supplied with power and whether thedevice is tripped or in the reset condition. When GFCI IC device 350 ispowered, e.g., via its voltage input port (LINE), which occurs when ACpower is connected to line terminals 326, 328, a voltage is generated atthe output port (VS). This voltage is dropped across zener diode 394,which is provided to maintain the voltage supplied to themicrocontroller within an acceptable level. Diodes 366, 368, connectedbetween the phase line conductor and power supply input port (LINE) ofGFCI IC 350 ensures that the voltage level supplied to GFCI IC and theVS output remain below approximately 30 volts. The voltage signaldropped across Zener diode 394 is connected to input port GP3 ofmicrocontroller 301. If microcontroller 301 does not measure a voltageat GP3, it determines that no power is being supplied by GFCI IC device350 and declares EOL.

Alternatively, if microcontroller 301 measures a voltage at GP3, itdetermines whether the device is tripped or in the reset state based onthe value of the voltage. For example, according to the circuit in FIG.4, if the voltage at GP3 is measured to be between 3.2 and 4.0 volts,e.g., between 76% of VCC and 100% of VCC, it is determined that there isno power at the face (342, 344) and load (346, 348) contacts and, thus,the device is in the tripped state. If the voltage at GP3 is between 2.4and 2.9 volts, e.g., between 51% of VCC and 74% of VCC, it is determinedthat there is power at the face and load contacts and the device is inthe reset state.

According to a further embodiment, when EOL is determined,microcontroller 301 attempts to trip interrupting device 315 in one orboth of the following ways: (a) by maintaining the stimulus signal onthird conductor 356 into the firing half-cycle of the AC wave, and/or,(b) by generating a voltage at an EOL port (GP2) of microcontroller 301.When EOL has been declared, e.g., because the auto-monitoring routinefails the requisite number of times and/or no power is being suppliedfrom the supply voltage output (VS) of GFCI IC device 350,microcontroller 301 produces a voltage at EOL port (GP2). Optionally,microcontroller 301 can also use the value of the input signal at GP3,as described above, to further determine whether the device is alreadyin the tripped state. For example, if microcontroller 301 determinesthat the device is tripped, e.g., the load and face contacts are notelectrically connected to the line contacts, microcontroller 301 maydetermine that driving SCR 369 and/or SCR 361 in an attempt to open thecontacts and trip the device is unnecessary and, thus, not drive SCR 369and SCR 361 via GP2.

The voltage at GP2 directly drives the gate of SCR 369 and/or SCR 361 toturn SCR 369 and/or SCR 361 ON, thus, enabling it to conduct current andactivate solenoid 362. More specifically, when SCR 369 and/or SCR 361are turned ON, current is drawn through coil 364 of dual-coil solenoid362. For example, dual-coil solenoid 362 includes inner primary coil364, which comprises an 800 turn, 18 Ohm, 35 AWG coil, and outersecondary coil 363, which includes a 950 turn, 16.9 Ohm, 33 AWG coil.Further details of the construction and functionality of dual-coil 362can be found in U.S. patent application Ser. No. 13/422,797, assigned tothe same assignee as the present application, the entire contents ofwhich are incorporated herein by reference for all that is taught.

As described above, when it is determined via the auto-monitoringroutine that detection circuit 352 is not successfully detecting groundfaults, e.g., it does not detect the flux resulting from current flowingin conductor 356, or it is not otherwise generating a drive signal atthe SCR_OUT output port of GFCI IC device 350 to drive the gate of SCR360 upon such detection, microcontroller 301 determines EOL and attemptsto trip interrupting device 315 by methods mentioned above.Specifically, microcontroller 301 attempts to directly trip directlydriving the primary coil 364, by the back-up path GP2 to SCR369 andSCR361. There is at least one difference, however, between the signal onconductor 356 when the auto-monitoring routine is being run normally,and the signal on conductor 356 generated when EOL is determined. Thatis, under EOL conditions, GP2 energizes both SCR361 and SCR 369 to betriggered and coil 362 and coil 363 to be energized, thus activatingsolenoid 362 and 369 to trip interrupting device 315.

If interrupting device 315 is opened, or if interrupting device 315 wasotherwise already open, power-on indicator circuit 321 will be OFF. Forexample, in the embodiment shown in FIG. 4, power-on indicator circuit321 includes LED 322 in series with resistor 323 and diode 324. Thecathode of LED 322 is connected to the neutral load conductor 278 andthe anode of diode 324 is connected to phase load conductor 277.Accordingly, when power is available at the load conductors, that is,the device is powered and in the reset state, current is drawn throughthe power-on circuit on each alternating half-cycle of AC power, thus,illuminating LED 322. If, on the other hand, power is not available atthe load conductors 277, 278, for example, because interrupting device315 is open, or tripped, or the device is reset but no power is beingapplied, LED 322 will be dark, or not illuminated.

Additional embodiments and aspects thereof, related to theauto-monitoring functionality consistent with the present invention, aswell as further discussion of some of the aspects already described, areprovided below.

The sinusoidal AC waveform discussed herein is connected to the phaseand neutral line terminals 326, 328 when the self-test GFCI device isinstalled correctly. According to one embodiment the AC waveform is a 60Hz signal that includes two half-cycles, a positive 8.333 millisecondhalf-cycle and a negative 8.333 millisecond half-cycle. The so-called“firing” half-cycle refers to the particular half-cycle, either positiveor negative, during which a gate trigger signal to SCR 360 results inthe respective gates of SCR 361 and SCR 369 being driven and thecorresponding respective solenoid coils 363, 364 conducting current,thus, “firing” solenoid 362 and causing the armature of the solenoid tobe displaced. A “non-firing” half-cycle refers to the alternatehalf-cycle of the AC waveform, i.e., either negative or positive, duringwhich current does not flow through the SCR or its respective solenoidcoil, regardless of whether or not the SCR gate is triggered. Accordingto the present embodiment, whether the positive or negative half-cycleis the firing half-cycle is determined by a diode, or some otherswitching device, placed in series with the respective solenoid coil.For example, in FIG. 4, diodes 359, 374 and 367 are configured such thatthe positive half-cycle is the “firing” half-cycle with respect to SCRs360, 369 and 361, respectively.

According to a further aspect of a circuit interrupting deviceconsistent with one or more embodiments, microcontroller 301 optionallymonitors the AC power input to the device. For example, the 60 Hz ACinput that is electrically connected to the phase and neutral lineterminals 326, 328 is monitored.

More particularly, a full 60 Hz AC cycle takes approximately 16.333milliseconds to complete. Thus, to monitor and confirm receipt andstabilization of the AC waveform, a timer/counter within microcontroller301 is implemented. For example, within the three (3) secondauto-monitoring window the 60 Hz input signal is sampled once everymillisecond to identify a leading edge, i.e., where the signal goes fromnegative to positive values. When a leading edge is detected a flag isset in the software and a count is incremented. When the three (3)second test period is finished, the count result is divided by 180 todetermine whether the frequency is within a specified range. Forexample, if the frequency is stable at 60 Hz, the result of dividing by180 would be 1.0 because there are 180 positive edges, and 180 cycles,in three (3) seconds worth of a 60 Hz signal. If the frequency isdetermined to not be within a given range, for example, 50-70 Hz, theauto-monitoring self-test fault testing is stopped, but the monitoringof GP3 continues. Accordingly, a premature or errant power failuredetermination is avoided when a circuit interrupting device inaccordance with the invention is connected to a variable power source,such as a portable generator, and the power source exhibits a lowerfrequency at start-up and requires a stabilization period before theoptimal frequency, e.g., 60 Hz, is achieved.

If the frequency is not stable at the optimal frequency, or at least notwithin an acceptable range, initiation of the auto-monitoring routine isdelayed until the frequency is stabilized. If the frequency does notachieve the optimal frequency, or a frequency within an acceptablerange, within a predetermined time, a fail tally is incremented. Similarto the fail tally discussed previously with respect to theauto-monitoring routine, if the tally reaches a given threshold,microcontroller 301 declares EOL.

As described above, according to at least one exemplary embodiment,programmable device 301 is implemented in a microcontroller. Becausesome microcontrollers include non-volatile memory, e.g., for storingvarious data, etc., in the event of a power outage, according to afurther embodiment, all events, timers, tallies and/or states within thenon-volatile memory are cleared upon power-up of the device.Accordingly, if the fail tally or other condition resulted from,improper device installation, inadequate or improper power, or someother non-fatal condition with respect to the circuit interruptingdevice itself, the fail tally is reset on power-up, when the tallyincrementing event may no longer be present. Another way of avoidingthis potential issue in accordance with the invention is to utilize aprogrammable device that does not include non-volatile memory.

While various embodiments have been chosen to illustrate the method anddevice disclosed herein, it will be understood by those skilled in theart that other modifications may be made without departing from thescope of the invention as defined by the appended claims.

What is claimed is:
 1. A wiring device comprising: a fault detectioncircuit configured to detect one or more fault conditions in said wiringdevice and generate a trigger signal when said fault condition meetspredetermined criteria; an actuating device with coaxial first andsecond conductive windings, wherein said second conductive winding iswound over said first conductive winding; and a first switching deviceactivated to turn on when said trigger signal is received from saidfault detection circuit; a second switching device including a firstpin, a second pin, and a third pin, said second switching deviceelectrically connected to said first conductive winding and said firstswitching device; and a third switching device including a first pin, asecond pin, and a third pin, said third switching device electricallyconnected to said second conductive winding and said first switchingdevice; wherein current flows through said first and second conductivewindings in response to said first switching device being turned on. 2.The wiring device as recited in claim 1, further comprising: said secondswitching device electrically connected to said first conductive windingand activated to draw current through said first conductive winding whensaid first switching device is turned on; and said third switchingdevice electrically connected to said second conductive winding andactivated to draw current through said second conductive winding whensaid first switching device is turned on.
 3. The wiring device asrecited in claim 2, wherein said actuating device includes a plungercoaxial with the respective axes of said first and second conductivewindings and a respective magnetic force is imparted on said plungerwhen each of said first and second conductive windings conducts current.4. The wiring device as recited in claim 3, wherein a third magneticforce is imparted on said plunger when both of said first and secondconductive windings conducts current simultaneously, said third magneticforce being greater than the sum of said first and second respectivemagnetic forces.
 5. The wiring device as recited in claim 1, whereinsaid third switching device blocks one or more feedback signalsgenerated by one or more of said first and second switching devices. 6.The wiring device as recited in claim 1, further comprising: whereinsaid fault detection signal is provided to cause said current flow; andan auto-monitoring circuit monitoring said current flow to determine anoperating state of said actuating device.
 7. The wiring device asrecited in claim 6, wherein said auto-monitoring circuit monitors afirst auto-monitoring input signal the value of which is at leastpartially determined by a value of a pre-trigger signal generated bysaid fault detection circuit, wherein said pre-trigger signal does notactivate said interrupting device to place said circuit interruptingdevice in said tripped condition.
 8. The wiring device as recited inclaim 7, wherein said fault detection circuit includes a GFCI devicethat detects a net current flowing from one or more line conductors toone or more load conductors and generates said pre-trigger signal whensaid net current exceeds a predetermined threshold.
 9. The wiring deviceas recited in claim 8, wherein said GFCI device generates a triggersignal to cause said current flow when said net current exceeds thepredetermined threshold for a predetermined amount of time.
 10. Thewiring device as recited in claim 7, wherein said pre-trigger signal isdelivered via a pre-trigger conductor.
 11. The wiring device as recitedin claim 10, further comprising a filter capacitor electricallyconnected between said pre-trigger conductor and electrical ground. 12.The wiring device as recited in claim 11, wherein the value of saidfilter capacitor is selected to eliminate noise from causing falsetrigger signals.
 13. The wiring device as recited in claim 1, whereinsaid fault detection circuit includes a 4141 GFCI chip.
 14. The wiringdevice as recited in claim 1, wherein the at least one selected from agroup consisting of the first switching device, the second switchingdevice, and the third switching device is a silicon controlled rectifierdevice.